1. Field of the invention
This invention relates to a developing process for electrophotography whereby a single-component non-magnetic toner is uniformly and reliably bound to an electrostatic latent image on the surface of a photoreceptor.
2. Description of the prior art
In a dry-type developing process for electrophotography, an excellent visible image results from the uniform and reliable formation of a toner layer on an electrostatic latent image on the surface of a photoreceptor. As a developer, there has been a two-component developer which is composed of a toner consisting of a variety of pigments, resin binders, etc., and a carrier giving charges to the toner; and a single-component developer consisting of a toner. For both developers, it is necessary for the toner to be uniformly and stably charge with electricity and the resulting charged toner should be uniformly and reliably transferred to the desired electrostatic latent image region on the photoreceptor.
The two-component developer is widely used since the toner therein can be easily produced and readily charged. The toner in the two-component developer is charged by friction with the carrier, and accordingly as the toner is consumed for the development treatment of the latent image, fresh toner must be supplied to maintain the amount of electric charge of the developer at a certain level. This oepration is quite troublesome and often difficult. When a certain amount of toner of the two-component developer is bound to the electrostatic latent image on the surface of the photoreceptor by means of a magnetic brush development, etc., the concentration ratio at the tip of the brush of the toner to the carrier must be maintained at a certain level. This is also quite difficult. Since the tip of the brush containing a rigid carrier composed of iron particles or glass beads is in contact with the surface of the photoreceptor, the surface of the photoreceptor becomes damaged. If the carrier is electroconductive, electric charges leak at the time when the carrier contacts the latent image on the photoreceptor resulting in a brush mark in the obtained visible image. In order to eliminate these drawbacks of the two-component developer, a non-contact development using a single-component developer has been recently proposed, wherein since a single-component toner is used, regulation of the toner concentration is not required and the control of supply of the toner is simplified. Especially, in a "jumping" development using a magnetic toner, the toner is fed to the surface of a photoreceptor by a "jumping" process, thereby forming an excellent visible image on the photoreceptor without damaging the surface of the photoreceptor. However, each of the toner particles must be charged using a sleeve having a specially treated surface to increase the charge efficiency of the sleeve and the toner, or using a corona charger. These charging methods give an insufficient and non-uniform amount of charge to the toner thereby creating a fog phenomenon and toner scattering, resulting in a visible image which is inferior in resolution.
On the other hand, in the preparation of a single-component toner, the dispersion of a magnetic material such as magnetite, etc. into a resin is so difficult that each of the obtained toner particles has a non-uniform magnetic force and a non-uniform diameter. Moreover, since the magnetic material is rigid, it tends to damage the surface of a photoreceptor when the surface of the photoreceptor is subjected to cleaning by means of a blade.